Levels of serum chemokines discriminate clinical myelopathy associated with human T lymphotropic virus type 1 (HTLV-1)/tropical spastic paraparesis (HAM/TSP) disease from HTLV-1 carrier state

Abstract

Approximately 5% of people infected with human T lymphotropic virus type 1 (HTLV-1) develop clinical myelopathy or tropical spastic paraparesis (HAM/TSP) that is associated with high-levels of Th1 cytokines, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha. Chemokines are known to induce cytokine secretion and direct the trafficking of immune cells to sites of disease. The present study measured serum chemokines correlated with autonomously released IFN-gamma in cell cultures. HTLV-1 infection was defined by enzyme-linked immunosorbent assay (ELISA) and confirmed by Western blot. Subjects included HTLV-1 carriers (n = 56), patients with HAM/TSP (n = 31) and healthy HTLV-1 seronegative volunteer controls (n = 20). Serum chemokines and IFN-gamma autonomously released by mononuclear cells in culture were quantified by ELISA. Compared to HTLV-1 carriers, serum chemokines in HAM/TSP patients showed significantly increased levels of CXCL9 and CXCL10, significantly diminished levels of CCL2 and similar amounts of CCL11 and CCL24. In contrast, CCL11 and CCL24 were significantly lower in serum of HAM/TSP patients than either control. IFN-gamma was positively correlated with CXCL9 and CXCL10 when HAM/TSP and HTLV-1 carriers were used as a combined group. However, despite a large proportion of HTLV-1 carriers having high IFN-gamma levels, these chemokines were not increased in carriers. This study showed that high levels of CXCL9 and CXCL10 in the systemic circulation and low serum CCL2 levels are features of HAM/TSP. HTLV-1 infection and Tax and/or additional viral encoded factor-mediated pathological processes triggering T cell activation with autogenous IFN-gamma release are probably involved in regulating chemokine release.

Fig. 1

Serum levels of type 2 chemokines, CXCL11 (a) and CXCL24 (b) are shown for healthy volunteers (n = 20) in human T cell lymphotropic virus (HTLV-1) carriers (n = 56) and in patients with HTLV-1/tropical spastic paraparesis (HAM/TSP) (n = 31). Mann–Whitney U-test was used for statistical analysis.

Fig. 2

Serum levels of CCL2 in patients with different clinical forms of human T cell lymphotropic virus (HTLV-1) infection [carrier, n= 56 and HTLV-1/tropical spastic paraparesis (HAM/TSP), n= 31] and in healthy subjects (n = 20). Mann–Whitney U-test was used for statistical analysis.

Fig. 3

Serum levels of CXCL9 (a) and CXCL10 (b) are shown for healthy volunteers (n = 20), in human T cell lymphotropic virus (HTLV-1) carriers (n = 56) and in patients with HTLV-1/tropical spastic paraparesis (HAM/TSP) (n = 31). Mann–Whitney U-test was used for statistical analysis.